Integrated circuits are required to operate at increasingly lower power supply voltages and increasingly higher speeds. Integrated circuits are often used in applications where low power consumption and high speed are important, such as in a battery powered computer system, or the like. An effective method for decreasing power consumption is to use a lower power supply voltage (for example, 3.3 volts). However, problems may be encountered when operating integrated circuits at 3.3 volts that were designed to be operated at 5.0 volts.
An input buffer is a gate that receives an input signal and isolates the input signal from a load. The input buffer may also restore the logic levels of the input signal, increase input signal margins, provide increased driving capability, and provide better noise immunity. An input buffer designed to be operated with a 5.0 volt power supply voltage may not operate effectively when a 3.3 volt power supply voltage is used, and overall performance of the integrated circuit may be degraded. For example, the margins of an input buffer may be affected if it is operated at other than the power supply voltage for which it was designed. That is, when a lower power supply voltage is used, reduced input margins, and decreased noise immunity may result. Also, the input buffer operated at reduced power supply voltages may not be capable of driving a large capacitive load without suffering a large voltage drop, which may further reduce margins. An input buffer operating with reduced margins may adversely affect the performance and reliability of the entire integrated circuit.